Pastry served in Mostar, tasty (4)
I believe the answer is:
tart
'pastry' is the definition.
(tart is a kind of pastry)
'in mostar tasty' is the wordplay.
'in' indicates a hidden word.
'TART' can be found hidden inside 'mostar tasty'.
'served' acts as a link.
(Other definitions for tart that I've seen before include "Open fruit pie" , "Professional woman" , "Somewhat sour like flat cake" , "Sharp; pastry" , "Sour -- acid" .)